Tpackard

I have a 1997 4.6 xlt. I had codes read at my brothers shop and they came back with
P0135-H025 B1S1 (heater circuit fault)
P0155-H025 B2S1 (heater circuit fault)
P0401 ( insufficient flow detected)
I replaced all four o2 sensors today but the same codes came back right away. After running it for a minute we cleared them again. This time they stayed off for about 15 minutes a driving. I shut the truck down, when I started it again after it cooled down the light is back on. Does anyone have any suggestions as to what might be causing this. I,understand how 02 sensors work and what the meaning of the code is.I am a little puzzled that new sensors didn't fix the problem.
Any help would be appreciated

Lx545

I would intepret that as insufficient cat flow or a bad wiring harness somewhere.

Tpackard

That's what I was leaning towards. I think I will start back tracking the wires first. If that doesn't work I'll hollow out the cat

Jbrew

Sounds like you would rather do more damage vs's fixing what's broke. Doubt we could keep up with yuh.

Tpackard

I would much rather fix what is broke then do any more damage to my rig. What would give you that idea? What would you recommend other than my plan to back trace the o2 wires looking for problems? Do you have a fundamental problem with hollowing out a Cat?

BareBonesXL

Don't O2 sensors have their own powered internal heater circuit? Seems like checking the power supply at the O2 plug would be in order. A new sensor will still have the same problem if it's the power supply to the sensor.

I searched "O2 sensor heater circuit" and this link came up. I'd take a meter to the O2 plug myself. No power, no sensor heating.

https://www.yourmechanic.com/article...by-jay-safford

Jbrew

I don't, why would I? Depending on the extent of exactly how you go about, your PCM might, - could have a problem mixing AF's thus making it yours.

If it was me and wasn't confident of repercussions my actions may cause, I would research. BareBonesXL has got you started there. Heater circuit wires are the two white wires. These O2's, all 4 sensors being identical w/different assignments. Black wire is signal (not ground), Grey wire is ground on these. This is a direct PCM ground.

That should get you started.

Tpackard

Thank you guys, we are all on the same page. I have been reading up as much as I could today, I found a wiring diagram for all four sensors to the PCM. The ground is the only common wire among the four going into the PCM so Hopefully that is it. I should have time tomorrow afternoon to play with it.

JLTD

I did a quick search on P0401...insufficient EGR flow. Have you changed anything with the EGR?

Jbrew

Right, the 401 DTC on the 4.6L's only (not the 5fours or V10) is usually plugged EGR ports. The 4sixes would benefit from a 5four set up, but Ford blessed the 4sixes with tiny ports creating the problem long-term. Runner up is a wet DPFE. The DPFE then corrodes (white rust) and shorts.